Nitrogen and mineral distribution in infant formulae

Abstract

Abstract Nitrogen and mineral distributions in infant formulae were compared to raw and pasteurized milk samples. The percentage of total nitrogen present in the fat fraction after centrifugation ranged from 20 to 50% among the infant formulae, whereas only 1.4% was found in the fat fraction of raw milk. Recovery of individual minerals from the three fractions exceeded 95% in all cases except for Zn, which exceeded 91%. Ca in the fat fraction of infant formulae ranged from 18 to 30%, whereas only 1.4–1.7% of the total Ca was recovered in the fat fraction of the raw milk and the pasteurized milk samples. P, Zn, Mg and Fe followed patterns similar to Ca. In contrast, 80–90% of the K and Na were found in the serum fraction of the infant formulae and milk samples. Electrophoretograms of the formulae showed that the proteins in the fat fraction were mainly caseins and β-lactoglobulin. The major proteins in the serum were β-lactoglobulin and α-lactalbumin with small casein bands. All the main proteins were found in the pellet. Electron micrographs of the formulae showed extensive attachment of denatured whey proteins and casein micelles to fat globule surfaces. Whey protein-casein micelle complexes were formed due to protein-protein interactions induced during processing. Electron-dense granules were also present on the lipid droplet surfaces and dispersed in the denatured whey proteins clusters and casein micelles of the infant formulae samples. Energy dispersive spectroscopy X-ray microanalysis of these electron-dense granules revealed the presence of K, P, Fe and Zn. These granules were not present in milk samples.